1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * Copyright (C) 2017 Joe Lawrence <joe.lawrence@redhat.com>
4 */
5
6/*
7 * livepatch-shadow-fix1.c - Shadow variables, livepatch demo
8 *
9 * Purpose
10 * -------
11 *
12 * Fixes the memory leak introduced in livepatch-shadow-mod through the
13 * use of a shadow variable.  This fix demonstrates the "extending" of
14 * short-lived data structures by patching its allocation and release
15 * functions.
16 *
17 *
18 * Usage
19 * -----
20 *
21 * This module is not intended to be standalone.  See the "Usage"
22 * section of livepatch-shadow-mod.c.
23 */
24
25#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
26
27#include <linux/module.h>
28#include <linux/kernel.h>
29#include <linux/livepatch.h>
30#include <linux/slab.h>
31
32/* Shadow variable enums */
33#define SV_LEAK		1
34
35/* Allocate new dummies every second */
36#define ALLOC_PERIOD	1
37/* Check for expired dummies after a few new ones have been allocated */
38#define CLEANUP_PERIOD	(3 * ALLOC_PERIOD)
39/* Dummies expire after a few cleanup instances */
40#define EXPIRE_PERIOD	(4 * CLEANUP_PERIOD)
41
42struct dummy {
43	struct list_head list;
44	unsigned long jiffies_expire;
45};
46
47/*
48 * The constructor makes more sense together with klp_shadow_get_or_alloc().
49 * In this example, it would be safe to assign the pointer also to the shadow
50 * variable returned by klp_shadow_alloc().  But we wanted to show the more
51 * complicated use of the API.
52 */
53static int shadow_leak_ctor(void *obj, void *shadow_data, void *ctor_data)
54{
55	int **shadow_leak = shadow_data;
56	int **leak = ctor_data;
57
58	if (!ctor_data)
59		return -EINVAL;
60
61	*shadow_leak = *leak;
62	return 0;
63}
64
65static struct dummy *livepatch_fix1_dummy_alloc(void)
66{
67	struct dummy *d;
68	int *leak;
69	int **shadow_leak;
70
71	d = kzalloc(sizeof(*d), GFP_KERNEL);
72	if (!d)
73		return NULL;
74
75	d->jiffies_expire = jiffies +
76		msecs_to_jiffies(1000 * EXPIRE_PERIOD);
77
78	/*
79	 * Patch: save the extra memory location into a SV_LEAK shadow
80	 * variable.  A patched dummy_free routine can later fetch this
81	 * pointer to handle resource release.
82	 */
83	leak = kzalloc(sizeof(*leak), GFP_KERNEL);
84	if (!leak)
85		goto err_leak;
86
87	shadow_leak = klp_shadow_alloc(d, SV_LEAK, sizeof(leak), GFP_KERNEL,
88				       shadow_leak_ctor, &leak);
89	if (!shadow_leak) {
90		pr_err("%s: failed to allocate shadow variable for the leaking pointer: dummy @ %p, leak @ %p\n",
91		       __func__, d, leak);
92		goto err_shadow;
93	}
94
95	pr_info("%s: dummy @ %p, expires @ %lx\n",
96		__func__, d, d->jiffies_expire);
97
98	return d;
99
100err_shadow:
101	kfree(leak);
102err_leak:
103	kfree(d);
104	return NULL;
105}
106
107static void livepatch_fix1_dummy_leak_dtor(void *obj, void *shadow_data)
108{
109	void *d = obj;
110	int **shadow_leak = shadow_data;
111
112	pr_info("%s: dummy @ %p, prevented leak @ %p\n",
113			 __func__, d, *shadow_leak);
114	kfree(*shadow_leak);
115}
116
117static void livepatch_fix1_dummy_free(struct dummy *d)
118{
119	int **shadow_leak;
120
121	/*
122	 * Patch: fetch the saved SV_LEAK shadow variable, detach and
123	 * free it.  Note: handle cases where this shadow variable does
124	 * not exist (ie, dummy structures allocated before this livepatch
125	 * was loaded.)
126	 */
127	shadow_leak = klp_shadow_get(d, SV_LEAK);
128	if (shadow_leak)
129		klp_shadow_free(d, SV_LEAK, livepatch_fix1_dummy_leak_dtor);
130	else
131		pr_info("%s: dummy @ %p leaked!\n", __func__, d);
132
133	kfree(d);
134}
135
136static struct klp_func funcs[] = {
137	{
138		.old_name = "dummy_alloc",
139		.new_func = livepatch_fix1_dummy_alloc,
140	},
141	{
142		.old_name = "dummy_free",
143		.new_func = livepatch_fix1_dummy_free,
144	}, { }
145};
146
147static struct klp_object objs[] = {
148	{
149		.name = "livepatch_shadow_mod",
150		.funcs = funcs,
151	}, { }
152};
153
154static struct klp_patch patch = {
155	.mod = THIS_MODULE,
156	.objs = objs,
157};
158
159static int livepatch_shadow_fix1_init(void)
160{
161	return klp_enable_patch(&patch);
162}
163
164static void livepatch_shadow_fix1_exit(void)
165{
166	/* Cleanup any existing SV_LEAK shadow variables */
167	klp_shadow_free_all(SV_LEAK, livepatch_fix1_dummy_leak_dtor);
168}
169
170module_init(livepatch_shadow_fix1_init);
171module_exit(livepatch_shadow_fix1_exit);
172MODULE_LICENSE("GPL");
173MODULE_INFO(livepatch, "Y");
174